1. Field of the Invention
The present invention relates generally to novel improvements in devices for mechanically receiving larger amounts of sound waves than are received by normal human ears alone. More particularly, it relates to such devices for directing these waves into the ears of a user in a manner that preserves the greatest possible degree of information contained in those sounds that is of interest to the user. This invention also allows the user to selectively block out other noises that could either interfere with the perception of the information-bearing sound, or even damage the user's hearing due to excessive sound pressure levels. While prior art describes devices that can also mechanically increase the amount of sound received by the ear, none would perform this function with the degree of acoustic fidelity of the present invention.
Given a maximum frontal opening dimension of the present invention's acoustic reflector of roughly two inches, sound wave diffraction prevents this size reflector from providing substantial sound wave amplification benefits for under three kiloHertz. However, this size reflector help to improve perception of all sounds down to half this frequency by lowering the resonant frequency of the human ear canal from three kiloHertz to fifteen hundred kilohertz; this is accomplished by the reflector acting as an extension to the ear's canal duct which effectively doubles its length and thus halves its resonant frequency. Frequencies of these rates upward provide listeners with important speech notes and musical instruments' fundamental tones, and most of the harmonic overtones that convey information regarding speech and music's details, sound source locations, and the ambient space in which the sound originates.
2. Description of the Prior Art
Researchers in related electroacoustic fields have identified such phenomena as sound wave phase incoherence and frequency group delays as causes for reduced information delivery by sound waves. Group delay causes a loss of natural realism to the perception of sounds, especially transients; in terms of measurements, group delay is plotted as the slope, or first derivative function of, phase shift versus frequency, showing the amount of time delay that is undergone by signal components in different segments of the frequency spectrum perceptible to humans. "Folded exponential horn" systems, such as described in Deutsches Reich Patentschrift Nr. 344526, issued Nov. 23, 1921 and U.S. Pat. No. 3,938,616, issued Feb. 17, 1976 to Brownfield, can cause sound waves to acquire these kinds of distortions, by causing excessive reflections and resonances within the amplifying device itself.
Testing of active transducers (stereo headphones) used in close proximity to the ear has revealed that ". . . sound pressure produced at the eardrum is critically dependant on the wave properties of the earphone and the external ear. The geometry of the cavities coupling the earphone to the ear drum, which is affected by such factors as the positioning of the earphone on the head of the listener, becomes the most critical issue. These wave effects become important . . . at frequencies above about 2,000 Hertz . . . (sound pressures at the eardrum are) critically dependant on the geometry of the earphone and ear and the exact positioning of the earphone . . . "; from a letter by Zwislocki, Kruger, Miller, Niemoeller, Shaw and Studebaker appearing in the April, 1988 issue of the Journal of the Acoustical Society of America.
A variety of additional hearing assistance devices and related structures are known in the art, which do not deal with the perceptible effects of the geometry of the invented device in relationship to the ear of the user. For example, hearing assistance devices including a cup configured for positioning behind and extending outward beyond the user's ear are shown in the following issued U.S. Pat. Nos. 1,708,257, issued Apr. 9, 1929 to Campbell; 1,820,107, issued Aug. 25, 1931 to Agee; 2,537,201, issued Jan. 9, 1951 to Amfitheatrof; U.S. Pat. No. 4,574,912, issued Mar. 11, 1986 to Fuss et al. Somewhat related structures in combination With eyeglasses are disclosed in U.S. Pat. No. 1,621,629, issued Mar. 27, 1927 to Dawson and U.S. Pat. No. 3,943,925, issued Mar. 16, 1976 to Leight. None of these prior art devices overcome the problems with such devices discussed above.
A device mounted about the ear for the purpose of amplification of sounds that are frontally incident to the user can have the additional benefit of blocking direct and reflected sounds from the user's sides and rear. The so-called Haas Precedence Effect causes sounds side-reflected to the listener's ears within a twenty millisecond interval of their generation by a sound source to the listener's front (as from the walls of the room in which the user is listening to an audio system's loudspeakers, or to a "live" performer) will reduce the listener's ability to accurately identify the location of the frontal sound sources on the basis of auditory cues alone. Such reflected sounds represent noise for the listener who wishes to make such localizations accurately. Such wall-or-side-reflected sound which is blocked by a device mounted around a user's ear can still cause such a device to "ring" in response, if it is not properly "damped" by fabrication from or with a material or materials which will prevent such sympathetic vibrations. Such ringing would serve as a noise source which could diminish the user's ability to accurately locate frontally-incident sound sources. Also, any likewise-undamped mechanical sound conduction between the base of such a noise-ringing device and the skin-covered temporal and mastoid bones around and behind the user's ear could transmit the ringing and noise of reflected sound into the user's auditory system, by means of bone conduction of contact-induced vibration. No means to prevent these unwanted transmissions is specified in the prior art. While Brownfield's U.S. Pat. No. 3,938,616 and Fuss et. al.'s U.S. Pat. No. 4,574,912, both mentioned above, do indicate means of cushioning such contact areas for greater user comfort, such pads are not designed to have the desirable effects of damping the device's ringing or of preventing induced temporal and mastoid bone sound conduction.